1. Field of the Invention
The present invention relates to a multilayered photodiode and a method of manufacturing the same, and more particularly, to a multilayered photodiode which converts incident light into an electrical signal, and a method of manufacturing the multilayered photodiode.
2. Description of the Related Art
A photodiode is a type of photosensor which converts light energy into electrical energy. When light strikes the diode, an electron and a positively charged hole are created, thereby producing current. The voltage of the current is substantially proportional to the intensity of light. Photodiodes have a high response speed, a wide sensitivity wavelength range, and superior photocurrent linearity.
The two commonly used types of photodiodes are PIN diodes and avalanche photodiodes (APDs). A PIN photodiode is a diode with an intrinsic semiconductor layer in the middle of a PN junction. Here, the intrinsic semiconductor layer has high resistance due to low carrier concentration. High speed characteristics of the PIN structure are obtained from a high electric field in the “I” layer rather than the PN junction. On the other hand, an APD includes an avalanche layer in the middle of a PN junction. In the APD, carriers generated by the excitation of incident light collide with atoms within an avalanche layer due to a high electric field, thereby creating hole-electron pairs. As the hole-electron pairs collide with each other, they bring abut an avalanche effect which, in turn, increases photocurrents. APDs based on this principle are used for long-distance telecommunication.
Photodiodes can be used in applications similar to those in which other photodetectors, such as photoconductors, charge-coupled devices (CCDs) and photomultiplier tubes, are used. They can be used in electronic devices such as compact disc players, fire alarms, and the receivers for remote controls in televisions. Furthermore, photodiodes are used for accurate measurement of light intensity in science and industry, and have a better, more linear response than photoconductors. Photodiodes are widely used in various medical applications such as detectors for computerized tomography or instruments to analyze samples.
A conventional photodiode, for example, a PIN photodiode, is a horizontal photodiode having a P-I-N structure in which a P-type doped region and an N-type doped region are situated on left and right sides of an insulating layer (I) which may be made of a silicon material.
In a horizontal photodiode, the amount of current generated from the same amount of received light increases as the distance between a P-type doped region and an N-type doped region increases, that is, as the width of the photodiode increases. In other words, the width of the photodiode should be increased in order to enhance current characteristics thereof. Therefore, horizontal photodiodes are not suitable for use in, for example, image sensor devices which are increasingly being required to become smaller. In addition, it is difficult to improve the performance of a horizontal photodiode while maintaining the width of the photodiode unchanged.
In this regard, a photodiode occupying a small area, but having improved current characteristics, is required.